1. Field of the Invention
The present invention relates generally to an acoustic touch position sensing system, and more particularly to a touch position sensing system with a large touch surface, wherein the system is capable of detecting a position of a touch on the surface without using large amplitude acoustic waves.
2. Description of the Related Art
Acoustic touch position sensing systems are known to include a touch panel having an array of transmitters positioned along a first edge of a substrate for simultaneously generating parallel acoustic waves that directionally propagate through the panel to an array of detectors positioned opposite the first array on a second edge of the substrate. Another pair of arrays is provided at appropriate angles to the first set.
When an object (e.g. a part of the human body like a finger, or a stylus, a bar) touch the surface of the substrate, the touch attenuates the acoustic waves passing through the point of the touch. The attenuation reflects the location of the point of the touch as shown in FIG. 2. Thus, the sensing system is capable of detecting the coordinates of the touch on the surface based upon the attenuated acoustic waves via the two sets of detectors.
One such acoustic touch position sensing systems is disclosed in U.S. Pat. No. 5,591,945 to Kent. The detailed description of this system is hereby incorporated by reference. The system employs shear wave propagation. Shear waves are (1) immune to noise created by asperities on the surface of the substrate and (2) have low attenuation. The attenuation of shear waves is ⅕ of the attenuation of common Rayleigh mode waves.
With reference to FIG. 1, the touch position sensing system 1 comprises a substrate 10 with a touch sensing surface, a controller 11, a burst signal generator 12, X/Y selectors 13 and 14, and a wave detector 15. The substrate 10 is a rectangular glass plate and has four reflective arrays 2X1, 2X2, 2Y1, and 2Y2 along each edge and also has transmitting transducers 3X1, and 3Y1 and corresponding receiving transducers 3X2 and 3Y2 which are placed on the four corners of the substrate 10, respectively. The touch sensing surface comprises the area enclosed by the four reflective arrays 2X1, 2X2, 2Y2, and 2Y2 in the substrate 10.
The reflective arrays 2X1, 2X2, 2Y1, and 2Y2 produce acoustic waves propagating at 90 degree to the original angle of transmission. The reflective arrays are formed of an acoustically partially reflective structure (grating) along its length. These reflective arrays may be formed on one or both sides of the substrate. Because the touch sensor is generally placed in front of a display device, the reflective arrays are generally placed at the periphery of the substrate, outside of the active sensing area, and are hidden or protected under a cover.
Each transducer 3X1, 3X2, 3Y1, and 3Y2 is connected to the surface to the substrate 10 via wedges 4X1, 4X2, 4Y1, and 4Y2. The transmitting transducer 3X1, generates longitudinal waves corresponding to the X coordinates of a touch position. The transmitting transducer 3Y1 generates longitudinal waves corresponding to the Y coordinates of a touch position. The generated acoustic waves are propagated on the surface of the substrate 10 via wedges 4X1 and 4Y1.
For example, in order for the system 1 to detect the X coordinate of a touch position, the controller 11 selects X/Y selector 13 and burst signals from the burst signal generator 12 are supplied to the X coordinate transmitting transducer 3X1. The supplied burst acoustic waves are propagated through the reference reflective array 2X1 via the wedge 4X1. Each grating of the reflective array 2X1 partially reflects the burst acoustic waves 90 degrees toward the opposite reflective array 2X2. The reference reflective array 2X2 reflects the propagating acoustic waves 90 degree toward the receiving transducer 3X2. The receiving transducer 3X2 receives each acoustic wave via the wedge 4X2 and converts the acoustic waves to electronic signals. The wave detector 15 detects both amplitude and time information of each received electronic signal corresponding to the propagating acoustic waves.
In order for the system 1 to detect the Y coordinate of a touch position, the controller 11 selects X/Y selector 13 and burst signals from the burst signal generator 12 are supplied to the Y coordinate transmitting transducer 3Y1. The supplied burst acoustic waves are propagated through the reference reflective array 2Y1 via the wedge 4Y1. Each grating of the reflective array 2Y1 partially reflects the burst acoustic waves 90 degrees toward the receiving transducer 3Y2. The receiving transducer 3Y2 receives each acoustic wave via the wedge 4Y2 and converts the acoustic waves to electronic signals.
The position of the touch in the active sensing area within the surface of the substrate 10 can be determined by providing an opposing reflective grating which directs the surface acoustic wave pattern along an axis of the grating toward a receiving transducer system. The touch sensing system 1 records the time of arrival of an attenuation of the wave pattern which corresponds to a position along the axis of the arrays. However, the larger the display size, the higher the transmitting loss of propagating acoustic waves.
The prior art system is effective for touch sensing areas as large as 50 inches. Today, however, there is a demand for a touch position-sensing system which can be used in conference rooms, classrooms or the like. In order for the prior art system to be used in this manner, the signal to noise ratio (SNR) of the detected acoustic waves must maintain at least a minimum certain value. Thus, the amplitude and pulse width of the transmitting acoustic waves must be large. Therefore, the prior art systems must apply a huge instantaneous voltage to an acoustic wave transducer. However, huge voltage can destroy acoustic wave transducers with normal endurance. On the other hand, if the prior art system employs an acoustic wave transducer with high endurance, the cost of the system becomes high.
Moreover, since the grating of the reflective array 2X1 reflect the acoustic waves supplied by the transmitting transducer 3X1, the amplitude of the reflected acoustic waves is decreased the further the grating is from the transmitting transducer 3X1 as shown in FIG. 3. Thus, when the touch surface is large, the reflected acoustic waves become too small at the gratings of the reference reflective array 2X1 which are too distant from transmitting transducer 3X1.
Accordingly, an object of the present invention is to overcome the above stated problems encountered in the aforementioned art.
This object and others are achieved according to the present invention by providing a touch position sensing system which includes a transducer configured to transmit and modulate by pseudo random coding acoustic waves and to decode reflected waves generated by the acoustic waves by autocorrelating the pseudo random coding; a substrate configured to propagate the acoustic waves, including a touch surface having a first axis along a side of the perimeter of the substrate and a second axis which is perpendicular to the first axis and located along a second side of the perimeter; and, a first reflective array configured to reflect the acoustic waves transmitted by the transducer such that reflected waves are generated traveling parallel to the second axis, having a length substantially as long as the side of the perimeter corresponding to the first axis including partially reflective grating along the length and disposed lengthwise along the first axis of said substrate. Wherein, a touch to the touch surface attenuates the reflected waves such that said modulation by pseudo random coding of acoustic waves is varied, the transducer configured to detect the location of the touch based on variation in autocorrelation of the varied pseudo random coding included in the reflected waves.
According to a second embodiment of the present invention, a touch position sensing system is disclosed including a processor configured to determine a location of a touch to the touch surface, wherein a touch to the touch surface varies the phase of the acoustic waves traversing the touch location and the processor is configured to determine the touch location based on a detected variation in the phase of the reflected waves.
Lastly, according to a third embodiment of the present invention, a touch position sensing system is disclosed including a transducer configured to transmit acoustic waves and to receive reflected waves generated by the acoustic waves; plural reflectors each configured to redirect incident acoustic waves 180 degrees; a substrate configured to propagate the acoustic waves, including a touch surface divided into quadrants by the transducer, a first reflector and a second reflector, each quadrant having orthogonal first and second axis; first reflective arrays extending along the first axis at opposite sides of said substrate, each including a reflective grating configured to reflect acoustic waves transmitted by the transducer in a direction parallel to the second axis in a respective quadrant, the first reflective arrays configured to reflect acoustic waves to the opposing one of said plural reflectors and receive acoustic waves redirected 180 degrees by the opposing reflector for each of quadrants. Wherein, a touch to the touch surface varies the amplitude of the acoustic waves traversing the touch location, said transducer configured to detect the touch location along the first axis based on a detected variation in the amplitude of acoustic waves redirected by the respective reflectors in each quadrant.